This disclosure relates to intermittently pressurized liquid pipelines which are drained of liquid when not pressurized. It is particularly applicable to movable pipelines which are drained to reduce their weight prior to movement.
This disclosure specifically illustrates application of the invention to portable sprinkler irrigation systems presently utilized in agriculture for distributing large volumes of irrigation water over adjacent field areas. Water is supplied under pressure from a main line connected to a pump and source of water. Water is distributed across the field through an elongated lateral pipeline. The lateral pipeline is selectively coupled to the main line through a control valve which can be opened or closed to control flow of water from the main line to the lateral pipeline. The lateral pipeline is typically connected at one end to the main line. The remaining end of the lateral pipeline is enclosed. A plurality of risers and sprinkler heads are arranged along the length of the lateral pipeline in hydraulic communication with its interior. They are selected and spaced to assure the desired distribution of water along adjacent field areas.
The portable lateral pipeline can be moved about the field in many different ways. If it rests directly on the ground, it can be dismantled and moved. However, it is advantageous to drag the pipeline lengthwise as a unit and eliminate the steps of dismantling and reconnecting the lateral pipeline sections. More commonly, the pipeline is supported on wheels or skids to permit it to be moved about the field in a direction perpendicular to its length. In a wheel move system, the pipe itself is the driving axle for the wheels. In a line move system, separate carriages support and move a nonrotatable lateral pipeline.
Most portable irrigation systems utilize lightweight conduit in the portable lateral pipeline and require draining of the lateral pipeline before it is moved, thereby minimizing the weight of the unit and the stresses encountered by the moving pipeline. Since the risers and sprinkler heads are directed upwardly from the lateral pipeline, water within the pipeline cannot drain through them by gravity when the supply valve has been closed. Automatic draining of portable lateral pipelines has been accomplished by providing pressure responsive valves along the bottom of the pipeline. Such valves are opened by springs when the water pressure decreases due to closing of the control valve. Since the water being dumped from the lateral pipeline by such valves might be deflected over a relatively small area under the drain valves, the result is an uneven distribution of water over a relatively small area and substantial waste of that volume of water filling the lateral pipeline at the time the system is shut down. In addition, after the pipeline has been moved and reconnected to the main line, it is necessary that the drain valves progressively close along the length of the lateral pipeline in response to the increase in pressure of the water flowing along its length. Another substantial volume of water is again wasted about small areas under the drain valves during the transition period as they are closing. The usage of such drain valves also results in wasted time during which the lateral pipeline is either being emptied or pressurized.